1. Field of the Invention
The present invention relates to processes and devices for monitoring the rotation of DC electric motors.
More particularly, the invention advantageously finds an application in respect of electric controls in motor vehicles and in particular in respect of the monitoring of the position and of the speed of an openable panel (electric window, sunroof panel, sliding door, etc.) controlled electrically with the aid of a DC electric motor or else in respect of the control of electric motors for ventilation, air-conditioning or heating of passenger compartments.
2. Description of Related Art
To date, the management of the position of a mechanism with DC motor is generally performed by one of the following means:
use of angular or linear incremental sensors (Hall effect for example) and counting of the pulses from the sensor,
detection of the end of travel positions (or the like) by sensors (electromechanical switches, inductive switches, etc.),
detection of mechanical abutments by measuring the current consumed.
The first solution has the drawback of requiring the use of expensive sensors.
Furthermore, the accuracy of the position thus determined is entirely dependent on the structure of the sensor and can vary greatly from one sensor to another.
Moreover, whereas one knows accurately the position which one seeks to determine at the instant at which a pulse is triggered, this position is known only rather inaccurately between each pulse.
The second solution has the drawback of requiring, likewise, the use of expensive sensors and of not allowing accurate determination of position between the markers of the sensors.
The third solution requires the use of mechanical abutments and detection of jamming current. The requirement of jamming in respect of detection gives rise to expensive dimensioning of the mechanical members which have to withstand the jamming stresses. Furthermore, here again, the position is uncontrolled between the positions of abutment.
An aim of the invention is to propose a solution which is reliable and economical and which makes it possible to accurately monitor the position of a movable element, and to do so over its entire travel.
Accordingly, it proposes a process for monitoring the rotation of a DC electric motor, wherein the voltage and the intensity of the current supplying said motor are measured in a manner sampled over time and wherein, for each sampling instant tn, an estimate xcex8n of the angular position is calculated as a function of a determined or known position for a previous sampling instant and of an estimate of a value of angular speed between these two instants, which is dependent on the voltage and on the intensity of current measured for the sampling instant tn and/or for one or more previous sampling instants.
Advantageously, an estimate of a value of angular speed xcexa9n at an instant tn is calculated from the equation:       Ω    n    =            (                        U          n                -                  RI          n                    )        Ke  
where Un and In are the measured values of the voltage and the intensity of the supply current at the sampling instant, where R corresponds to the equivalent resistance of the motor, where Ke is the parameter of proportionality between the speed of rotation of the shaft of the motor and the electromotive force generated by the rotation.
In particular, in respect of an instant tn, an estimate xcex8n of the angular position is determined by:             θ      n        -          θ              n        -        1              =            (                                    Ω            n                    +                      Ω                          n              -              1                                      2            )        ⁢          (                        t          n                -                  t                      n            -            1                              )      
where nxe2x88x921 is the index of the sampling instant tnxe2x88x921 just prior to the instant tn.
According to one possible mode of implementation, during a startup, an estimate of the value of the resistance R is determined by calculating:   R  =      ax    ⁢          U              I        peak            
where Ipeak is the maximum intensity of current measured during a startup, U is the measured supply voltage corresponding to this intensity of current, and a is a given coefficient.
According to another mode of implementation, an estimate of the value of the resistance R is determined by calculating:   R  =            1                        ∫          1          t2                ⁢                  I          ⁢                      ⅆ            t                                ⁢          (                                    ∫            1            t2                    ⁢                      U            ⁢                          ⅆ              t                                      -                  K          ⁢                      xe2x80x83                    ⁢          e          ⁢                      xe2x80x83                    ⁢          σ                    )      
where "sgr" is the angle which separates the positions corresponding to two markers of determined positions, t1 and t2 corresponding to the two instants at which these two markers are crossed. In particular then, to determine this estimated value, one calculates:   R  =            1                                    ∑                          tn              =              t1                        t2                    ⁢                      I            n                          ⁣                              ·            Δ                    ⁢                      xe2x80x83                    ⁢          t                      ⁢          (                        ∑                      t            =            t1                    t2                ⁢                  (                                                                      U                  n                                ·                Δ                            ⁢                              xe2x80x83                            ⁢              t                        -                          K              ⁢                              xe2x80x83                            ⁢              e              ⁢                              xe2x80x83                            ⁢              σ                                )                    )      
where
In is the sampled value of the current for t=tn
Un is the sampled value of the voltage for t=tn
and where xcex94t is the sampling period.
Preferably, an estimate of the temperature of the electric motor is determined as a function of the estimate of the value of the resistance R and, according to the value of the temperature thus estimated, the supply to the electric motor is cut.
A device in accordance with the invention comprises measuring means and calculating means for implementing the aforesaid process.
Preferably, the calculating means comprise a microcontroller which drives the electric motor.
Advantageously, this device comprises means for, as a function of the speed and of the angular position which are calculated at each sampling instant, controlling the electric motor so as to avoid excessive pinchings.
As a variant or as an adjunct, it comprises means for, as a function of the speed and of the angular position which are calculated at each sampling instant, speed-slaving the movement of the openable panel.
As a variant or as an adjunct likewise, it comprises means for, as a function of the speed and of the angular position which are calculated at each sampling instant, controlling the electric motor in such a way as to obtain accurate positioning of the openable panel.
Another object of the invention is to propose a system for controlling motor vehicle openable panels comprising a DC electric motor, which comprises a device of the aforesaid type.